I'm a software engineer. On multiple occasions over the years I have witnessed my own computers doing very similar things to what hers is doing in her poorly shot video (landscape, not portrait!).
In every case, it was caused by a hardware problem. Either the keyboard just went bad, or I had recently spilled something into the keyboard, or something was pressing keys on a wirelessly (and out of sight/mind) connected keyboard.
At no time did it turn out to be that my computer had been hacked.
If I had hacked into her computer for the purposes of intimidating her, I'd have sent:
Command-A (select all)
Command-X (cut)
We are watching you!
Command-A (select all)
Command-V (paste)
In her case, it looks like Command-Z (two keys which are kitty-corner from each other on both my Macbook, and the bluetooth keyboard I use with it) is being held down (undo), so all of her previous typing and formatting gets undone.
It didn't even have to be two keys. A stuck backspace key would have caused exactly what was shown on her video of the supposed "hack"